Hydrochloric acid/hydrofluoric acid treatment to remove asbestos fibers from a well bore

ABSTRACT

An aqueous mixture of hydrochloric acid and hydrofluoric acid is employed to accomplish the 98 percent disintegration of chrysotile asbestos. In a specific embodiment an aqueous mixture of hydrochloric acid and hydrofluoric acid is injected into a well to remove chrysotile asbestos injected into the well in a well-working fluid.

United States Patent 1 1 Wally 1 51 Jan. 2, 1973 54 HYDROCHLORIC2,225,695 12 1940 Henderson 61 al ..252 s.55 c

ACID/HYDROFLUORI ACID 2,663,689 12/1953 Kingston 6:31... TREATMENT ToREMOVE ASBESTOS 2: 5:21? FIBERS FROM A WELL BORE 3:184:288 5/1965Lisle.......::::::::... [75] Inventor: Robert F. Wally, Bartlesville,Okla. 3,297,516 1/1967 Naufilann 3,458,393 7/1969 Battista [73]Assignee: Phillips Petroleum Company 3,543,856 12/1970 Knox et a1.3,650,886 3/1972 Torok [22] June 231 1971 3,652,382 3 1972 Gancy [21]Appl. No.: 156,091

Primary Examiner-Stephen J. Novosad Attorney-J. Arthur Young et al. [52111.8. C1. ..166/307, 134/3, 166/312,

252/855 C 57 ABSTRACT [51] Int. Cl.....E2lb 43/27, E21b 43/28, C03b37/00 581 Field 61 Search ..166/307, 281, 271, 311, 312; 3 hydmchlmc.acld and 252/8 55 23/91 88 110 P 110 162/3. hydrofluonc acid isemployed to accomplish the 98 134/3 41 percent disintegration ofchrysotile asbestos. In a specific embodiment an aqueous mixture ofhydrochloric acid and hydrofluoric acid is injected [56] ReferencesClted into a well to remove chrysotile asbestos injected into UNITED TET NTS the well in a well-working fluid. 112,650 3/1871 Stevens ..23/110p 4 Claims, No Drawings HYDROCHLORIC AClD/ll-IYDROFLUORIC ACID TREATMENTTO REMOVE ASBESTOS FIBERS FROM A WELL BORE BACKGROUND OF THE INVENTIONThis invention relates to dissolving asbestos in aqueous acid solutions.In one of its aspects, this invention relates to removing inorganicmineral well-working additives from well bore holes. In another of itsaspects, this invention relates to removing well plugging materials froman oil well bore hole. In one of its concepts, this invention relates toremoving inorganic mineral plugs from oil well bore holes. In another ofits concepts, this invention relates to removing asbestos oil welladditives from oil well bore holes.

Asbestos fibers have been used to control the viscosity and carryingcapacity of drilling muds, to stop seepage loss in work-over muds, andlonger fibers of chrysotile asbestos have been used as lost circulationmaterial. In the latter two uses cited above the fibers are used toblock flow into the pores of the well. The use of asbestos fiber as alost circulation material has never had much acceptance because nomethod of removing it from the producing zone existed if the lostcirculation occurred in zones of possible production. Asbestos fibersare almost completely inert. Contamination does not affect the fiber nordo microorganisms degrade it. Because of its inertness, asbestos fiberhas been considered acid resistant. Because of this assumption some welloperators have rejected the use of asbestos fiber in their work-over andcompletion fluids. It has been thought that the fibers would plug thepores of the producing formation and could not be removed. Priorliterature, while not finding asbestos inert, would certainly lead oneto believe that asbestos fiber could be damaging to the production of awell. S. Speil and J. P. Leineweber in Asbestos Minerals in ModernTechnology, Johns Manville Research and Engineering Center,Environmental Research, Volume II, No. 3, April, 1969, show thatchrysotile asbestos is between 50 and 60 percent soluble in boiling HClof either four normal or 25 percent normal. They also show thatregardless of the type of mineral acid used there is very littledifference in the solubility of chrysotile asbestos. Therefore, evenunder the best conditions described by Speil and Leineweber almost 40percent residue would be left after asbestos fiber had been treated withHCl. If plugging were a problem, a residue of approximately 40 percentwould still leave considerable formation damage.

Surprisingly, l have found that an aqueous solution of a combination ofacids can dissolve 98 percent of an agglomeration of chrysotile asbestosfibers.

It is therefore an object of this invention to provide a method fordissolving chrysotile asbestos fibers. It is another object of thisinvention to provide a method for removing chrysotile asbestos fibersfrom oil wells to which they have been added in the production of thewell.

Other concepts, objects and the several advantages of this invention areapparent from a study of this disclosure and the appended claims.

In accordance with the invention a method for disintegrating solidchrysotile asbestos is provided which comprises mixing, at a temperatureand for a time sufficient to react the chrysotile asbestos, thechrysotile asbestos and a mixture of hydrochloric acid and hydrofluoricacid in proportions to supply at least a stoichiometrically idealreactive amount of hydrochloric acid and hydrofluoric acid per unit ofchrysotile asbestos to be reacted.

In one embodiment of the invention chrysotile asbestos injected into awell bore in a well-working operation is removed from the well bore byinjecting into the well an aqueous solution containing a combination ofhydrochloric acid and hydrofluoric acid and circulating this solutionfor a time sufficient to dissolve the chrysotile asbestos.

The chrysotile asbestos that is disintegrated by the method of thisinvention has a general fgi m la M g Si O 5(OI-I)4 and physically isdescribed as cylindrical filuils. These fibers have been described asconsisting of layers of silicon-oxygen tetrahedra condensed on tomagnesium hydroxide layers with each siliconoxygen/magnesium hydroxidelayer superimposed on layers of similar composition. There is somemechanical interlocking between the layers but no chemical bonding.

Stoichiometrically the acid solubility of chrysotile asbestos may beexpressed as follows On a pound basis, one pound of asbestos cantheoretically be dissolved using 0.78 pounds hydrochloric acid and 0.58pounds hydrofluoric acid. In actual operations the strength of the acidsolutions used would be adjusted for the safest and most efficient useat the site of the well being treated. In standard operations a ratio ofweight percent hydrochloric acid to weight percent hydrofluoric acid inaqueous solution of 30:1 to 4:1 can be used with a range of 15:1 to 5:1being preferred.

The following example is presented to show the disintegration ofchrysotile asbestos fibers according to the process of this inventionand is meant to be illustrative and not exclusive.

EXAMPLE I One gram of asbestos fiber was added to 200 ml. of acid in abeaker for each test. The samples were aged at various temperatures withoccasional stirring. At the end of the aging period the samples werefiltered, washed with 200 ml. of water, dried in an oven, and theresidue weighed. All weighing was done on a Mettler balance with anaccuracy of 10.01 gram. The aqueous solution of acids was prepared fromhydrochloric acid, reagent grade 36 percent and hydrofluoric acid,technical grade 52 percent. In all tests 15 percent by weighthydrochloric acid in aqueous solution was used. The weight percenthydrofluoric acid is marked in the table showing the results. Theasbestos fibers tested were Flosal, a chrysotile asbestos used as adrilling mud additive, trademarked to Drilling Specialties Company, andasbestos grades 3F, 32, 4H, 5D, 6D and 7D of the Johns Manville Companywhich are varying lengths of chrysotile asbestos fibers as specified bythe Quebec (Canada) Standard Test issued by the Quebec Asbestos MiningAssociation.

TABLE I EFFECTS OF l-ICl ON FLOSAL Asbestos Sample Asbestos Sample Thistable shows the effect of a percent by weight aqueous hydrochloric acidsolution on a one gram sample of the type chrysotile asbestos used in adrilling mud formulation. It should be noted that the percent solubilityagrees closely with the figures quoted by Speil and Leineweber above.

TABLE II EFFECT OF HCl AND HF ON FLOSAL Asbestos Sample Asbestos SampleTime Final Weight Weight loss HF HCl Hrs. g weight weight l .02 98 2.]l5 4 .02 98 2.l l5 6 .02 98 2.1 15 24 .02 98 2.1 15 l .02 98 1.5 15 l.02 98 L0 15 l .17 83 0.5 15 4 .02 98 0.5 15 6 .02 98 0.5 15

All tests were run at 75F (22 C) This table, contrasted to the Table 1above, shows the effectiveness of the aqueous solution of mixed acids ofthis invention in disintegrating asbestos fiber. As shown in this table,98 percent of the asbestos is dissolved in a reasonable time by the acidmixture, whereas only approximately 60 percent of the asbestos could bedissolved by hydrochloric acid alone. i

TABLE III 4 EFFECT OF HCl AND HCHF ON ASBESTOS FIBER Asbestos SampleAsbestos Sample Time Final Weight Weight Loss Asbestos Grade Hrs. g A.l5% HCl- 176F (C) 18 .47 53 3F 18 .48 52 3Z I8 .47 53 4H 18 .47 53 5D 18.48 52 6D 18 .49 51 7D 8. 15% HCl-2.1% HF This table contrasts theeffectiveness of a mixture of hydrochloric acid and hydrofluoric acid inaqueous solution as an agent for dissolution of various asbestos fiberswith the ability of hydrochloric acid alone to dissolve only about halfof the fiber sample over a much longer period of time.

Reasonable variation and modification are possible within the scope ofthe foregoing disclosure and the appended claims to the invention, theessence of which is that hydrochloric acid and hydrofluoric acid incombination in aqueous solution can be used to disintegrate chrysotileasbestos fibers and thereby effectively remove from a well bore holeasbestos fibers that have been injected into the well in a drilling orproducing operation.

I claim:

l. A method for disintegrating solid chrysotile asbestos comprisingmixing the chrysotile asbestos at a temperature and for a timesufficient to react the chrysotile asbestos with an aqueous solution ofa mixture of hydrochloric and hydrofluoric acid in proportions to supplyat least the stoichiometric ideal reactive amount of hydrochloric acidand hydrofluoric acid per unit of chrysotile asbestos to be reacted.

2. A method for removing chrysotile asbestos from a well bore comprisinginjecting into the well an aqueous solution of a mixture of hydrochloricacid and hydrofluoric acid with circulation for a time sufficient todissolve the chrysotile asbestos by the method of claim 1.

3. The method of claim 2 wherein the ratio of weight percenthydrochloric acid to weight percent hydrofluoric acid is in the range of30:1 to 4:1.

4. The method of claim 1 wherein the combination of acids is comprisedof 15 percent by weight hydrochloric acid and 2.1 percent by weighthydrofluoric acid.

2. A method for removing chrysotile asbestos from a well bore comprisinginjecting into the well an aqueous solution of a mixture of hydrochloricacid and hydrofluoric acid with circulation for a time sufficient todissolve the chrysotile asbestos by the method of claim
 1. 3. The methodof claim 2 wherein the ratio of weight percent hydrochloric acid toweight percent hydrofluoric acid is in the range of 30:1 to 4:1.
 4. Themethod of claim 1 wherein the combination of acids is comprised of 15percent by weight hydrochloric acid and 2.1 percent by weighthydrofluoric acid.